1. Field of the Invention
The present invention relates in general to a vehicular automatic transmission, and more particularly to a structural improvement of a vehicular automatic transmission, which permits an improvement in the efficiency of assembling of the vehicular automatic transmission.
2. Discussion of Related Art
There has been a growing need of improving the efficiency of assembling of a vehicular automatic transmission, to satisfy a recently increasing number of manufacture of motor vehicles. In a conventional method of assembling of the vehicular automatic transmission, all parts of the automatic transmission are assembled on a main assembling line, so that the required length of the main production line tends to increase with an increase of the required number of assembling steps, with a result of an increase of the required installation space for the main assembling line. A shut-down of the main assembling line due to shortage of any part or an assembling error at a local portion of the main assembling line results in interruption of all assembling steps and a consequent drop of productivity of the automatic transmission. JP-8-170699 A discloses an example of a technique to simplify the main assembling line and reduce a risk of the shut-down of the main assembling line for thereby improving the productivity of the automatic transmission. According to this technique, frictional coupling elements of a frictional coupling device in the form of a brake are mounted on a rear casing of the automatic transmission, so that the frictional coupling elements can be assembled on the automatic transmission on a sub-assembling line.
Some motor vehicles of different configurations use the same type of automatic transmission, which use casings of respective different configurations. Although the rear casing and the related parts can be assembled into a subassembly, this subassembly cannot be used for the motor vehicles of the different configurations using the same type of automatic transmission. In this respect, the conventional vehicular transmission has a room for further improvements. Usually, the accuracy of machining of the rear casing is not high except for its surfaces in contact with a main casing of the automatic transmission. However, the rear casing to be assembled together with its related parts according to the technique disclosed in the above-identified publication requires a higher degree of accuracy of machining to form an oil chamber for a piston of the brake, and a splined portion engaging the above-indicated frictional coupling elements in the form of friction plates, for example. Thus, the technique in question requires the rear casing which should be manufactured with the high degree of accuracy at a relatively large number of its structural portions, and accordingly requires a larger number of machining steps and additional jigs for the machining steps.